The present invention relates to a device for computing interpolated values for a waveform, digitally generated in an electronic device, by using only amplitude values of the waveform.
A variety of devices for digitally generating waveforms have been developed. Particularly in the field of electronic musical instruments, it is frequently required to generate a sine wave or a cosine wave. In such a case, the wave data are initially stored in a ROM (read only memory). The ROM is addressed to read out the waveform data therefrom. In a waveform generating device as disclosed in Kokai No. 57/142698, the amplitude value of a sine wave or a cosine wave at a predetermined sampling point, and the difference between this amplitude value and the amplitude value at a sampling point adjacent to the former point, are stored in a ROM. The difference of the amplitude values is subjected to a linear approximation in a multiplier to obtain interpolated values. The interpolated value thus obtained is used for gaining an amplitude value at a mid point between the sampling points. In storing the sine waveform data or the cosine waveform data in the ROM, the lesser amount of the data to be stored, the better. Nevertheless, in the conventional device, two types of data, i.e., the amplitude value data and the difference data, must be stored; therefore, the memory capacity of the ROM is increased.